Crystallization of Supramolecular Complexes as an Alternative Route for the Separation of Racemic p‐X‐phenylethanol

A partial chiral discrimination of racemic p‐halogenated derivatives of phenylethanol is observed during the crystallization in water of host‐guest supramolecular compounds with permethylated β‐cyclodextrin. Enantioenrichment with this chiral host is however highly sensitive to crystallization durations and to the chemical nature of the halogenated substituent of the guest. Structural determinations performed for the complexes formed with (R) and (S) p‐bromo‐phenylethanol indicate that stereodifferenciation for this guest is associated to distinct inclusion features. The understanding of the underlying chiral recognition mechanisms, the careful design of suitable crystallization conditions, and the use of a procedure involving successive crystallizations allows to envisage a complete resolution of racemic mixtures by means of supramolecular complexations.